In conventional magnetic recording, thermal instabilities of the stored magnetization in the recording media can cause loss of recorded data. To avoid this, media with high magneto-crystalline anisotropy (Ku) are required. However, increasing Ku also increases the coercivity of the media, which can exceed the write field capability of the write head. Since it is known that the coercivity of the magnetic material of the recording layer is temperature dependent, one proposed solution to the thermal stability problem is heat-assisted magnetic recording (HAMR), wherein high-Ku magnetic recording material is heated locally during writing by the write head to lower the coercivity enough for writing to occur, but where the coercivity/anisotropy is high enough for thermal stability of the recorded bits at the ambient temperature of the disk drive (i.e., the normal operating or “room” temperature of approximately 15-30° C.). In some proposed HAMR systems, the magnetic recording material is heated to near or above its Curie temperature. The recorded data is then read back at ambient temperature by a conventional magnetoresistive read head, i.e., a giant magnetoresistance (GMR) or tunneling magnetoresistance (TMR) based read head. HAMR disk drives have been proposed for both conventional continuous media, wherein the magnetic recording material is a continuous layer on the disk, and for bit-patterned media (BPM), wherein the magnetic recording material is patterned into discrete data islands or “bits”.
One type of proposed HAMR disk drive uses a laser source and an optical waveguide coupled to a transducer, e.g., a near-field transducer (NFT), for heating the recording material on the disk. A “near-field” transducer is an optical device with subwavelength features that is used to concentrate the light delivered by the waveguide into spot smaller than the diffraction limit and at distance smaller than the wavelength of light. In a HAMR head, the NFT is typically located at the air-bearing surface (ABS) of the slider that also supports the read/write head and rides or “files” above the disk surface while creating the sub-diffraction-limited optical spot on the disk.
A problem with writing of data in a HAMR disk drive is that several microseconds are required to stabilize the laser power once the laser is turned on. However, in conventional disk drives the gap length between data sectors where the data is to be written corresponds to only several hundreds of nanoseconds. This is insufficient time for the laser power to stabilize prior to writing to the data sectors by the write head. Thus the use of much longer gaps for each data sectors means there is a large loss of disk real estate.
What is needed is a HAMR disk drive and method for writing to the data sectors that does not result in loss of disk real estate.